Process for treating a body of stainless steel so as to promote its adherence to a rubber composition

ABSTRACT

Process for treating a body of steel to promote its adherence to a composition which includes at least a rubber, containing the following points: 
     a body at least the surface of which is of stainless steel is used, this steel containing at least 0.02% and at most 0.2% carbon, at least 3% and at most 20% nickel, at least 12% and at most 28% chromium, the sum of the nickel and the chromium being at least equal to 20% and at most equal to 35%, all of these percentage values being by weight; the structure of the steel includes at least 20% by volume of martensite and is without austenite or it comprises less than 80% thereof by volume; 
     the surface of the body is activated and then treated with at least one starting silane so that it is covered with a film constituted only, or substantially only, of one or more silanes, in such a manner that this surface treated in this way can be placed directly in contact with the composition. 
     Articles comprising a rubber composition and a metal body which has been treated in accordance with the process of the invention, such articles being for instance tires.

This is a divisional of allowed application Ser. No. 08/620,489 filedMar. 22, 1996, now U.S. Pat. No. 5,789,080.

BACKGROUND OF THE INVENTION

The present invention relates to processes which permit adherencebetween metal bodies and rubber, these metal bodies being in particularreinforcements used to reinforce rubber articles which may, forinstance, be various manufactured articles such as tubes, plies, beltsor tires, the metal reinforcements being, for instance, wires,assemblies of wires, or bead rings.

The invention also relates to the articles obtained by these processes.

The invention relates, very particularly, to the case in which the metalbodies are of stainless steel.

It is known to incorporate metal compounds, in particularly cobaltcompounds, into rubber compositions in order to favor the adherence ofthe metal reinforcements to rubber. Such compounds are described, forinstance, in French A-2 198 830, and U.S. Pat. No. 2,912,355.

This technique has the following drawbacks:

the metal compounds extensively modify the working properties and theperformance of the vulcanized compositions, in particular the resistanceto thermal and thermo-oxidizing aging is substantially altered;furthermore, the incorporating of these compounds in the compositions iscostly and the metals of these compounds may at times be scarce;

the adherence can, in general, be obtained only on copper, zinc, brassor bronze surfaces, so that it is necessary to effect a coating withthese metals or alloys on the metal reinforcement when the latter is ofa different constitution, for instance when it consists of steel, whichis very commonly used for the reinforcements; such a metal coating isdifficult to effect on stainless steel surfaces, since it is thengenerally necessary to apply a sub-coat, for instance of nickel, beforeeffecting this coating;

the adherence performances of the reinforcements obtained are at timesinsufficient and one can note, in particular, poor adhesion at hightemperatures, degradation over the course of time and/or with respect tocorrosion, in particular corrosion in the presence of water.

It is known to use coatings of brass formed by an electrolytic orchemical deposit of copper and zinc, this brass which has diffused wellpermitting a bonding to compositions which contain low concentrations ofcobalt compound or which may even be without such compounds. Thesecoatings have the drawback of being more difficult to produce than theaforesaid coatings and the bonding thus obtained is of poor resistanceto thermal aging or thermo-oxidizing aging, for instance in the presenceof water.

U.S. Pat. No. 4,441,946 and French A-2 320 974 describe a process foradhering steel to a rubber composition by applying a silane to thesurface of the steel before placing it in contact with the composition.Stainless steels are not mentioned in those documents.

SUMMARY OF THE INVENTION

The present invention relates to a process for causing a specialstainless steel to adhere in a simple and economical manner to a rubbercomposition without the steel being coated with a metal materialdifferent from steel and without it being necessary for the compositionto contain an organo-metallic compound which favors adherence, theadherence being capable of taking place however even in the presence ofsuch a compound.

The process of the invention for treating a steel body so as to favorits adherence to a composition comprising at least one rubber comprisesthe following points:

a body is used at least the surface of which is of stainless steel, thissteel containing at least 0.02% and at most 0.2% carbon, at least 3% andat most 20% nickel, at least 12% and at most 28% chromium, the sum ofthe nickel and chromium being at least equal to 20% and at most equal to35%, all these percentage values being by weight; the structure of thesteel comprises at least 20% by volume martensite and is withoutaustenite or it comprises less than 80% thereof by volume;

the surface of the body is activated and then treated with at least onestarting silane so that it is covered with a film constituted only, orsubstantially only, of one or more silanes, in such a way that thissurface treated in this manner can be placed directly in contact withthe composition.

The starting silane preferably has the formula: ##STR1## in which Rrepresents an organic radical containing at least one function capableof reacting with at least one element of the composition; each OR'represents a group capable of reacting with an oxide or hydroxide of thesurface of the stainless steel; each R" represents, independently,hydrogen, a cyclic or acyclic organic radical, or a halogen; a, whichcan be zero, is equal to at most 2.

R can, for instance, comprise at least one function capable of reactingwith at least one rubber of the composition, or with at least one resincontained in the composition, or with at least one other componentcontained in the composition.

R is preferably a hydroxyalkyl, an aminoalkyl, a polyaminoalkyl, anepoxyalkyl, in particular a glycidylalkyl, a haloalkyl, a mercaptoalkyl,an alkyl sulfide or an alkyl polysulfide which may contain a siliconatom, an azidoalkyl, or a cyclic or acyclic radical comprising at leastone double bond.

Each R' is, for instance, independently, hydrogen or a cyclic or acyclicorganic or organometallic radical.

When R' is an organometallic radical, it preferably comprises at leastone silicon atom.

Each R' is preferably, independently, hydrogen, an alkyl having from 1to 6 carbon atoms, an organometallic radical comprising 1 to 6 carbonatoms, and at least one silicon atom.

Each R" is preferably, independently, an alkyl having from 1 to 6 carbonatoms.

a is preferably equal to zero or 1.

Examples of these compounds which can be used are3-aminopropyl-triethoxysilane, 3-glycidoxypropyl-trimethoxy-silane,3-mercaptopropyl-trimethoxysilane,N-beta-aminoethyl-3-aminopropyl-trimethoxysilane,3-aminopropyl-trimethoxy-silane, 3-aminoethyl-triethoxysilane,3-glycidoxyethyl-triethoxysilane, 3-mercaptopropyl-triethoxysilane,N-beta-aminoethyl-3-aminoethyl-trimethoxysilane,3-aminobutyl-triethoxysilane, 3-aminoethyl-trimethoxysilane,3-amino-propyl-methyl-diethoxysilane, bis-triethoxy-silylpropyltetrasulfide, bis-trimethoxy-silylpropyl tetrasulfide,p-(trimethoxy-silyl)benzyl diazoacetate, 4-(trimethoxysilyl)cyclohexyl-sulfonyl azide, 6-(trimethoxysilyl)hexylsulfonyl azide.

Preferred compounds are 3-aminopropyl-triethoxysilane,N-beta-aminoethyl-3-aminopropyl-trimethoxysilane,3-glycidoxypropyl-trimethoxysilane, 3-mercaptopropyl-trimethoxysilane,and 3-aminopropyl-methyl diethoxysilane.

3-aminopropyl-triethoxysilane is particularly preferred.

A single silane or a mixture of silanes may be used.

The silane is preferably soluble in water or in a mixture of water andalcohol, such a solution permitting for instance the hydrolysis of thestarting silane.

The composition can for instance be the composition to which the body isintended to adhere, in particular in order to reinforce it, or it canform an adhesive intermediate layer arranged directly in contact withthe body so as to adhere then to another rubber composition which thebody is for instance to reinforce; the composition which serves to formthe adhesive intermediate layer may then for instance be present in theform of a solution or a suspension in one or more organic solvents or inthe form of an aqueous suspension. The adhesive intermediate layer mayalso be formed, for instance, by directly extruding the composition ontothe surface of the body, in particular with an extruder, the compositionthen preferably being in a viscous or pasty form, but not in the form ofa solution or a suspension. The use of such an adhesive may have theadvantage of simplifying the formulating of the composition which it isdesired to reinforce.

The invention also concerns articles comprising a rubber composition anda metal body treated in accordance with the process of the invention.These articles are, for instance, tubes, belts, and tires.

The rubber of the composition is preferably an unsaturated rubber, forinstance natural rubber or a synthetic rubber. Examples of suchsynthetic rubbers are polyisoprene, polybutadiene, polychloroprene,butyl rubber, styrene-butadiene copolymers,acrylonitrile-butadiene-styrene copolymers, EPDM(ethylene-propylene-diene) terpolymers. However, the rubber or rubbersof the composition may also be saturated, for instanceethylene-propylene copolymers. These rubbers may be cross-linked forinstance under the action of sulfur, peroxides or bismaleimides, with orwithout sulfur, the cross-linking agents being incorporated in thecomposition where they can be without cross-linking system, such as forinstance thermoplastic rubbers.

The composition may comprise a single rubber or a mixture of at leasttwo rubbers of the same type or different types; for example, it maycomprise a mixture of an unsaturated rubber and a saturated rubber.

The composition may furthermore comprise the customary fillers andadditives, such as, for instance, carbon black, silica, stearic acid,zinc oxide, vulcanization accelerators, anti-aging agents, in particularantioxidants, oils or agents which facilitate the working, andreinforcing resins, in particular resins of the phenol-formol orresorcinol-formol type.

The metal body is preferably a reinforcement, for instance a wire, aribbon, an assembly of wires and/or of ribbons, in particular a cable ora bead ring.

The silane is preferably used in the form of a solution, theconcentration of the silane in the solution being, for instance, between0.05% by weight and 10% by weight, and preferably between 0.1% by weightand 5% by weight. In certain cases, a slight acidification of thesolvent improves the performance of the organosilane.

It is necessary that the surface of the body be activated before contactwith the silane. This activation can be effected in various ways knownin the art, for instance by a chemical treatment, preferably an acidtreatment, or a physical treatment, preferably a plasma treatment. Thesurface of the body is preferably activated by an aqueous acid solution,for instance aqueous phosphoric acid. A sulfochromic bath can also beused for this purpose.

After this activation, the surface can, for instance, be rinsed withwater and dried in air.

It should be noted that there is concerned here a true activationtreatment which modifies the stainless steel surface without it beingpossible to determine precisely the nature of this change which may takeplace, for instance, by the formation of non-stoichiometric hydroxidesor oxides of nickel and chromium. There is not concerned here a simplecleaning, for instance a washing, intended to remove dirt or impuritiesfrom the surface of the stainless steel without modifying it. It is,however, preferred also to wash the surface, particularly in theproduction of thin wires by wire drawing, either before the activationtreatment or during the period of activation, for instance by using atreatment with an acid bath containing a surface-active agent, such abath permitting these two operations simultaneously. The depositing ofthe silane on the body can be obtained by any known process, continuousor discontinuous, for instance an application with a brush, by dipping,or by spraying.

After the application of the silane, the surface of the body can forinstance be dried in ambient air or by heating in a furnace or a tunnel,the heating being for instance obtained by conduction in contact withhot gas or electrically, in particular, by joule effect or by induction.This heating permits the departure of the solvent or solvents if any, aswell as the reaction of at least one silane with the stainless steelsurface of the body; it also permits the cross-linking of the silane orsilanes and therefore the formation of a silane polymer network to forma film which is without, or practically without, compounds other thansilanes.

The body thus treated in accordance with the invention can be placeddirectly in contact with the rubber composition, without adhesive layer,this composition possibly containing a known reinforcing resin ofphenol-formol or resorcinol-formol type in a concentration of, forinstance, 0.1 to 20% by weight of the composition, and preferablybetween 1 and 8 by weight of the composition. For example, if the silaneselected contains an amine function, the rubber composition willpreferably contain a reinforcing resin of phenol-formol type or a resinof resorcinol-formol type, the formol being possibly replaced by othermethylene donors, such as hexamethylene tetramine (HMTA) orhexa(methoxymethyl)melamine (H3M). In the event that the silane reactswith a resin, this reaction preferably takes place upon thevulcanization of the rubber, if the rubber is vulcanizable.

If the silane selected contains a mercapto, polysulfide, azide or alkenefunction, the composition may then contain a simple cross-linking system(for instance sulfur, a vulcanization accelerator, a peroxide), thesilane then reacting directly with the rubber upon the vulcanization.

When the composition is used as adhesive, this adhesive isadvantageously used, in known manner, either in the form of a solutionor a suspension in one or more organic solvents, or in the form of anaqueous suspension, said solution or suspension then preferablycontaining a reinforcing resin, or else by direct extrusion of thecomposition onto the

When the adhesive is in the form of a solution or a suspension, thesolvent or solvents are preferably alkanes, for instance heptane, ordistillation cuts of petroleum, and/or aromatic compounds, for instancetoluene.

When the adhesive is in the form of an aqueous suspension, it isobtained preferably, in known manner, by mixing one or more latexes ofone or more rubbers with an aqueous solution of one or moreresorcinol-formol precondensates, which gives a known adhesive of RFLtype formed solely of an aqueous solution of the resin or resinscontaining the rubber or rubbers in suspension.

The dry extract of the solution or suspension generally comprisesbetween 5% and 30% and preferably between 10 and 15% by weight.

The adhesives can, for instance, be applied to the body by the sametechniques as those mentioned previously for the application of thesilane.

The adhesives described above can be dried, for instance, by means of afurnace or tunnel at a temperature of preferably between 100° C. and250° C. for a period of time of, for instance, between 10 seconds and 10minutes.

When the composition is used as adhesive to favor the bonding betweenthe body and another composition, for instance a composition to bereinforced by the body, this other rubber composition may be a knowncomposition without any special, preferential limitation with respect toits various components and such limitations are not indicated forreasons of simplification.

In all the cases cited above, the reinforcing resins may, if applicable,be obtained in situ upon the curing of the composition, the latter thencontaining, before the curing, the basic components of said resin, forinstance resorcinol and a hardener such as HMTA.

The adherence between the metal and the rubber composition is obtainedat the end of the curing of this composition, which is preferablyeffected under pressure. Furthermore, the reactions mentioned above ofthe silanes with the stainless steel as well as said cross linkings ofthe silanes may possibly take place at least partially upon this curing.

DESCRIPTION OF PREFERRED EMBODIMENTS Definitions and Tests

1. Dynamometric Measurements.

The measurements of resistance to rupture, rupture force and elongationupon rupture of the steel wires are carried out in traction inaccordance with AFNOR method NF A 03-151 of June 1978.

2. Torsional Ductility

By definition, the torsional ductility of a wire is the number of turnsof twisting on itself that the wire can withstand. This measurement iseffected on a length of wire equal to 500 times its diameter. One end ofthis wire is held in a fixed jaw and the other end is held in a rotaryjaw which is rotated in such a manner that the axis of rotation is thesame as the axis of the wire, the tension upon this twisting being equalto 5% of the rupture force in tension of the wire measured beforetwisting, and the number of turns necessary in order to cause therupture of the wire are counted.

3. Structure of the Steels.

The identification and quantification of the structure of the steels areeffected in the following manner:

An X-ray diffraction method is employed. The method used consists ofdetermining the total diffracted intensity for each of the phases of thesteel, in particular the α' martensite, the .di-elect cons. martensite,and the gamma austenite, totalling the integrated intensity of all thediffraction peaks of this phase, which makes it possible to calculatethe percentages of each of the phases with respect to the total of allof the phases of the steel.

The X-ray diffraction spectra are determined on the section of wire tobe studied with a goniometer, using a chromium anticathode.

Sweeping makes it possible to obtain the characteristic lines of each ofthe phases present. In the case of the three phases mentioned above (thetwo martensites and the austenite), the sweep is 50 degrees to 160degrees.

In order to determine the integrated intensities of the peaks, it isnecessary to deconvolute the interfering rays.

The following relationship applies for each peak of any phase:

I_(int) =(L_(mh) ×I_(max))/P in which:

I_(int) =the integrated intensity of the peak

L_(mh) =the width at mid-height of the peak (in degrees)

I_(max) =the intensity of the peak (in counts per second)

P=the measurement pitch of the peak (0.05 degrees).

One has, for example, the following characteristic lines:

    ______________________________________                                        Gamma austenite                                                                             line (111)   2θ =                                                                           66.8                                                      line (200)   2θ =                                                                           79.0                                                      line (220)   2θ =                                                                           128.7                                       α' martensite                                                                         line (110)   2θ =                                                                           68.8                                                      line (200)   2θ =                                                                           106                                                       line (211)   2θ =                                                                           156.1                                       ε martensite                                                                        line (100)   2θ =                                                                           65.4                                                      line (002)   2θ =                                                                           71.1                                                      line (101)   2θ =                                                                           76.9                                                      line (102)   2θ =                                                                           105.3                                                     line (110)   2θ =                                                                           136.2                                       ______________________________________                                    

The angle 2θ is the total angle in degrees between the incident beam andthe diffracted beam.

The crystallographic structures of the preceding phases are as follows:

Gamma austenite: face centered cubic α' martensite: body centered cubicor body centered tetragonal ★ martensite: hexagonal.

One can then calculate the percentage by volume of any phase "i" by thefollowing relationship:

    % of phase "i"=I.sub.i /I.sub.t

in which:

I_(i) =sum of the integrated intensities of all the peaks of said phase"i"

I_(t) =sum of the integrated intensities of all the peaks of all thediffraction phases of the steel.

One therefore has, in particular:

% of α' martensite=I.sub.α' /I_(t)

% of .di-elect cons. martensite=I.sub..di-elect cons. /I_(t)

total % of martensite=(I.sub.α' +I.sub..di-elect cons.)/I_(t)

% of gamma austenite=I_(gamma) /I_(t)

with:

I.sub.α' =integrated intensity of all the peaks of α' martensite

I.sub..di-elect cons. =integrated intensity of all the peaks of.di-elect cons. martensite

I_(gamma) =integrated intensity of all the peaks of gamma austenite.

In the following, the different percentages concerning the phases of thestructure of the steel are expressed in volume and the terms"martensite" or "martensite phase" cover all of the α' martensite and.di-elect cons. martensite phases, the term % martensite thereforerepresenting the % by volume of the total of these two martensiticphases and the term "austanite" represents gamma austenite.

The percentages by volume of the different phases, determined by thepreceding method, are obtained with a precision of about 5%.

4. Bonding Measurements

The bonding measurements are carried out on metal reinforcements whichare either isolated wires or assemblies of wires.

The quality of the bond between a metal reinforcement and a rubbercomposition is assessed by a test in which one measures the forcenecessary to extract the reinforcements from the vulcanized composition,also known as vulcanizate. The vulcanizate is a block of rubber formedof two plates of a size of 300 mm×150 mm and a thickness of 3.5 mm,applied one to the other before curing (the thickness of the resultantblock is therefore 7 mm). Upon the making of this block, thereinforcements, twelve in number, are interposed between the two rawplates and only a reinforcement length of 1 cm is then left free to comein contact with the composition to which this reinforcement length willbe bonded during the curing. The rest of the length of the reinforcementis covered by a thin film of aluminum in order to prevent any adherencebeyond the 1 cm zone. The block containing the reinforcements is thenplaced in a suitable mold and cured under a pressure of 11 bars.

The temperature and the curing time of the block are a function of thedesired test conditions, as indicated below.

Simple Curing

The block is heated to a temperature of 140° C. or 150° C. for a periodof time which may range from 30 minutes to 2 hours, under a pressure of11 bars.

Overcuring (thermal stability)

The overcuring, effected instead of the simple curing, is a treatmentwhich makes it possible to determine the resistance of the samples toheat alone. The block is heated at 140° C. for 6 hours under a pressureof 11 bars.

Thermal Aging in Humid Phase

This treatment makes it possible to determine the resistance of thesamples to the combined action of heat and water.

After the simple curing, the samples are placed in an atmosphere ofsaturated steam at 110° C. for 16 hours.

At the end of the simple curing or of the overcuring, or the thermalaging in humid phase, the block is cut into test specimens serving assamples, each containing a reinforcement, which is placed under tractionby means of a traction machine. The traction rate is 50 mm/min.

The adherence is thus characterized by the force necessary to pull thereinforcement from the test specimen (pulling force) at 20° C. (averageof 12 measurements corresponding to 12 reinforcements).

II. EXAMPLES

The invention will be easily understood by means of the followingnon-limitative examples.

In all these tests, all the data concerning the formulations of therubber or resin compositions are parts by weight, unless otherwiseindicated.

IIA. Examples on Isolated Wires

In all these cases, identical wires of stainless steel are used havingthe following composition:

C: 0.08; Cr: 18.3; Ni: 8.75; Mo: 0.3; Mn: 0.8; Si: 0.75; Cu: 0.3; N:0.04; S: 0.001; P: 0.019; the balance being formed of iron with theinevitable customary impurities. All these figures concerning thecomposition of the steel are in per cent by weight. The structure ofthis steel comprises more than 50% by volume martensite and less than50% by volume austenite.

These wires have the following properties: diameter: 1.3 mm; resistanceto rupture 2250 MPa; elongation upon rupture: 1%.

These wires are prepared by work hardening of a machine wire ofstainless steel of austenitic structure, this machine wire having adiameter of 5.5 mm.

These wires are used as is (each of them is therefore referred tosubsequently as "bare wire") or with a coating of brass applied over acoating of nickel in the control tests not in accordance with theinvention (each of them is then referred to subsequently as"brass-coated wire"). The brass used is a brass made by the electrolyticco-deposition of copper and zinc containing 69% copper, which brass canbe used to bond compositions without cobalt compounds. The thickness ofthe coating is equivalent to 52 mg of brass for 100 g of wire.

The three known compositions of rubber which is follow are used in theseexamples.

Composition 1

This composition, which contains a reinforcing resin, has the followingformulation:

    ______________________________________                                        Natural rubber   100                                                          Black N326       75                                                           Zinc oxide       6                                                            Stearic acid     1                                                            Antioxidant      1 - Phenol-formol resin 4                                    Sulfur           6                                                            Sulfenamide      1                                                            Hardener         1.6                                                          ______________________________________                                    

Composition 2

This composition, which is without reinforcing resin, has the followingformulation:

    ______________________________________                                               Natural rubber                                                                         100                                                                  Black N326                                                                             45                                                                   Zinc oxide                                                                             8                                                                    Stearic acid                                                                           0.5                                                                  Antioxidant                                                                            1                                                                    Sulfur   6                                                                    Sulfenamide                                                                            1                                                             ______________________________________                                    

Composition 3

This composition contains a reinforcing resin and a natural rubber/SBRblend. It has the following composition:

    ______________________________________                                               Natural rubber                                                                           50                                                                 SBR        50                                                                 Black N326 60                                                                 Zinc oxide 8                                                                  Stearic acid                                                                             0.5                                                                Antioxidant                                                                              1                                                                  Phenol-formol resin                                                                      8                                                                  Hardener   3                                                                  Sulfur     7                                                                  Sulfenamide                                                                              1                                                           ______________________________________                                    

In the three above compositions, the following definitions apply:

SBR: Styrene-butadiene copolymer prepared in solution with analkyl-lithium catalysis, this copolymer comprising 26% styrene and 74%butadiene, the butadiene phase comprising 24% 1-2 vinyl bonds. The glasstransition temperature (Tg) of the copolymer is -48° C. and its Mooneyviscosity (100° C.) is 54.

Black N326: Designation in accordance with ASTM Standard D-1765.

Antioxidant: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

Sulfenamide: N-dicyclohexyl-2-benzothiazole sulfenamide.

Phenol-formol resins: Precondensate of Type SFP 118 (Schenectadycompany)

Hardener: Hexamethylene tetramine (HMTA).

The three compositions are without adherence promoter of cobalt-salttype.

Example 1 (not in accordance with the invention)

A bare wire is treated at 50° C. for 30 seconds with an aqueousphosphoric acid solution of a pH of 1 (concentration by weight, ofphosphoric acid about 2.5%) containing a surface-active agent(Ultraspeed 4353 solution of the Condat company, Chasse sur Rhone,France, diluted to 10% by volume), then rinsed with water and dried inambient air.

The adhesion test is then carried out between the bare wire treated inthis manner and composition 1, after simple curing effected for 60minutes at 150° C. A pulling force of 5 daN is obtained.

This test shows that the adherence is poor.

Example 2 (not in accordance with the invention)

The adherence test is carried out between a brass-plated wire andcomposition 1 after simple curing for 60 minutes at 150° C. A pullingforce of 96 daN is obtained.

This test shows that the adherence is better than in the precedingexample, due to the presence of the brass.

Example 3 (not in accordance with the invention)

The adherence test is carried out between a brass-plated wire andcomposition 1 after overcuring for 6 hours at 140° C. The pulling forceis 70 daN.

This test shows that the overcuring causes a substantial decrease in theadherence, this decrease being about 27%.

Example 4 (not in accordance with the invention)

The adherence test is carried out between a brass-plated wire andcomposition 1 after curing for 60 minutes at 150° C. followed by thermalaging in humid phase.

The pulling force determined in this manner is 7 daN.

This test shows that the adherence suffers a considerable decrease afterthe treatment by thermal aging in humid phase, this decrease being about93%

Example 5 (in accordance with the invention)

A bare wire is treated in the same manner as in Example 1, except thatafter the air drying, it is immersed in a 90/10 (by volume)ethanol/water solution of 3-aminopropyl-triethoxysilane (concentrationof about 1% by weight) and dried for 1 minute at 160° C. The adherencetest is then carried out between the wire which has been treated in thisway and composition 1 after simple curing for 60 minutes at 150° C.

The pulling force obtained is 72 daN, which is to say it is acceptable.The acid treatment solution permits both the cleaning of the metalsurface and its activation before the treatment with silane. After thetreatment with silane, the metal surface is covered by a film formedentirely or practically entirely, by cross-linked silane.

Example 6 (in accordance with the invention)

The adherence test is carried out between a bare wire treated as inExample 5 and the composition 1 after overcuring for 6 hours at 140° C.

The pulling force obtained s 69 daN, that is to say there is practicallyno decrease as compared with Example 5.

Example 7 (in accordance with the invention)

The adherence test is carried out between a bare wire treated inaccordance with Example 5 and the composition 1 after simple curing for60 minutes at 150° C. and thermal aging in humid phase.

The pulling force obtained is 65 daN.

It is noted that the decrease in this force as compared with Example 5is very slight, since it is about 10%.

Example 8 (not in accordance with the invention)

The adherence test is carried out between a brass-coated wire andcomposition 2, after simple curing for 90 minutes at 140° C. A pullingforce of 90 daN is obtained.

Example 9 (not in accordance with the invention)

The adherence test is carried out between a brass-coated wire andcomposition 2 after overcuring for 6 hours at 140° C. Practically thesame pulling force is obtained as in Example 8, probably as a result ofthe absence of resin in composition 2.

Example 10 (not in accordance with the invention)

The adherence test is carried out between a brass-coated wire andcomposition 2 after simple curing for 90 minutes at 140° C. and thenafter thermal aging in humid phase. A pulling force of 25 daN isobtained. The decrease as compared with Example 8 is therefore about72%, in other words very substantial.

Example 11 (in accordance with the invention)

A bare wire is treated as in Example 5, with the difference that anaqueous solution of silane is used.

An adhesive of type RFL is then deposited by dipping on the wire treatedin this manner.

The synthesis of the adhesive is effected in two steps.

First Step

In this step, a resin solution having the following formula is formed:

    ______________________________________                                        H.sub.2 O           100                                                       Formaldehyde, 31% in water                                                                        14.7                                                      Resorcinol          8.1                                                       Solution of 1 Mol/1 NaOH                                                                          5.9                                                       ______________________________________                                    

The precondensation of the resin is effected for 4 hours at roomtemperature.

Second Step

In this second step, an aqueous suspension is produced from thepreceding precondensate and a latex, the composition of the suspensionbeing as follows:

    ______________________________________                                        H.sub.2 O           100                                                       Latex, 40% in water 34.6                                                      Precondensate       23.5                                                      Solution of NH.sub.4 OH d = 0.92                                                                  4.1                                                       ______________________________________                                    

The rubber of the latex is a vinylpyridine-styrene-butadiene terpolymercontaining 15% vinylpyridine units. Its surface tension is 47.5 mJ/m²and its Mooney viscosity at 100° C. is 37.

The characteristics of the adhesive prepared in this manner are:

Mass percentage of dry extract of the resin=10%;

Resin-mass/dry-extract mass of the latex=0.17;

Number of moles of formol/number of moles of resorcinol=2;

Number of moles of NaOH/number of moles of resorcinol=7.5×10⁻².

Upon this second step, the postcondensation is carried out for 16 hoursat room temperature.

The adhesive applied onto the wire is dried for 3 minutes at 150° C. Theadherence test between the wire which has been treated in this mannerand composition 2 is then effected after simple curing for 90 minutes at140° C. The pulling force thus obtained is 86 daN, which issubstantially the same as Example 8.

Example 12 (in accordance with the invention)

A bare wire is treated as in Example 11. The adherence test is thencarried out between the wire treated in this manner and composition 2,after overcuring for 6 hours at 140° C. There is thus obtained a pullingforce of 79 daN, which represents a decrease of about 8 as compared withExample 11, which is very slight.

Example 13 (in accordance with the invention)

The adherence test is carried out between the wire treated in accordancewith Example 11 and composition 2 after a simple curing effected for 90minutes at 140° C. and after thermal aging in humid phase. There is thusobtained a pulling force of 36 daN, which represents a decrease of about58% as compared with Example 11, namely a much smaller decrease than inExample 10.

IIB. Examples with Reinforcement Assemblies

In the examples which follow, assemblies of wires were used asreinforcement and their adherence in contact with a rubber compositionwas measured.

The assemblies are formed of stainless steel wires having the followingcomposition:

C: 0.096; Cr: 17.6; Ni: 7.7; Mo: 0.7; Mn: 1.3; Si: 2.0; Cu: 0.2; N:0.04; S: 0.001; P: 0.019; the balance being formed of iron with theinevitable customary impurities. All of these figures concerning thecomposition of the steel are % by weight.

The wires which constitute the assemblies are in accordance withEuropean Patent Application No. 94115799.2 and French Patent ApplicationNo. 9412372, which applications are incorporated by reference in thepresent application. These wires have the following properties:

For Examples 14 to 25:

diameter: 0.224 mm; resistance to rupture: 2805 MPa; rupture force: 110N; elongation upon rupture: 1%; torsional ductility: 60 turns;structure: martensitic phase practically equal to 85% by volume, thisphase consisting practically exclusively of α' martensite, the austenitephase being practically 15% by volume.

For Examples 26 to 28:

diameter: 0.18 mm; resistance to rupture: 2500 MPa; rupture force: 63.6N; elongation upon rupture: 1%; torsional ductility: 70 turns;structure: martensitic phase practically equal to 57% by volume, thisphase consisting practically exclusively of α' martensite, the austenitephase being practically 43% by volume.

These wires are used in the assemblies either as is (each of them isthen referred to subsequently as "bare wire") or with a coating of brassin the control tests not in accordance with the invention (each of thembeing then referred to subsequently as "brass-coated" wire). The brassused is a thermal brass containing 64% copper. This brass is produced bythermal diffusion after depositing of a layer of copper followed by adeposit of a layer of zinc. This brass is intended to be used to bondrubber compositions containing cobalt compounds. The thickness of thebrass coating is equivalent to 0.19 μm on the fine wire, after wiredrawing, the brass-coating being effected on a thin layer of nickelpreviously deposited directly in contact with the stainless steel,before wire drawing.

In examples 14 to 25 which follow, assemblies which are all of the sametype, designated 6×23NF, are used.

Each of these assemblies, without hoop, is formed in three strands, eachstrand being formed of two wires twisted together with a pitch of 12.5mm, the twist of the wires of one strand being effected in directionopposite that of the wires of the other two strands, all of thesestrands being twisted together with an assembly pitch of 12.5 mm, thedirection of winding of the assembly being the same as the direction ofwinding of the wires in the two strands the wires of which are wound inthe same direction.

In Examples 26 to 28, assemblies of type 19.18, not hooped, are used,each assembly being an assembly of layers the characteristics of whichare as follows:

an untwisted core wire;

an intermediate layer of six wires wound around the core, with a pitchof 10 mm;

an outer layer of twelve wires wound around the intermediate layer inthe same direction as said intermediate layer, with a pitch of 10 mm.

In Examples 14 to 25 which follow, the compositions 1, 2 or 3 describedabove are used, with the difference that in the case of the assemblieswith brass-coated wires, these compositions comprise furthermore onepart by weight of cobalt naphthenate to 100 parts by weight of elastomer(composition 1 or 2) or elastomer blend (composition 3).

Example 14 (not in accordance with the invention)

The adherence test is carried out between an assembly formed ofbrass-coated wires and composition 1, after simple curing for 60 minutesat 150° C. A pulling forc e of about 48 daN is thus determined.

Example 15 (not in accordance with the invention)

The adherence test is carried out between an assembly formed ofbrass-coated wires and composition 1, after overcuring for 6 hours at140° C. A pulling force of 39 daN is then determined. The decrease ascompared with example 14 is about 19%.

Example 16 (not in accordance with the invention)

The adherence test is carried out between an assembly formed ofbrass-coated wires and composition 1, after simple curing for 60 minutesat 150° C. followed by thermal aging in humid phase.

The pulling force is 28 daN.

This test shows that the adherence experiences a considerable decreaseafter the thermal aging treatment in humid phase, this decrease beingabout 42%.

Example 17 (in accordance with the invention)

An assembly of bare wires is treated as in Example 5. Thereupon, anadhesive of solution type having the following formula is deposited bydipping on the assembly of wires treated in this manner:

    ______________________________________                                        Natural rubber     100                                                        Black N326         47                                                         Silica             8                                                          Zinc oxide         5                                                          Stearic acid       2                                                          Antioxidant        1                                                          Resorcinol-formol resin                                                                          5                                                          Sulfur             3                                                          Sulfenamide        1                                                          Hardener           5                                                          ______________________________________                                    

Antioxidant, sulfenamide and hardener: Same characteristics as forcompositions 1, 2, and 3.

Silica of Ultrasil VN3 type (Degussa company)

Resorcinol-formol resin: Precondensate of type SRF 1500 (Schenectadycompany).

The composition is dissolved in heptane, the concentration of solidsbeing equal to 10% by weight.

The adhesive is dried for 3 minutes at 160° C.

The adherence test is then carried out between the assemblies of wirestreated in this manner and composition 2 after simple curing for 90minutes at 140° C.

A pulling force equal to 42 daN is then obtained.

Example 18 (in accordance with the invention)

An assembly of bare wires is treated in the same manner as in Example17. The adherence test is then carried out between the assembliestreated in this manner and composition 2 after simple curing for 90minutes at 140° C., followed by thermal aging in humid phase.

The pulling force thus determined is 46 daN. There is therefore nodecrease as compared with Example 17.

Example 19 (in accordance with the invention)

An assembly of bare wires is activated by the same phosphoric acidsolution as in Example 1, at 50° C. for 30 seconds, whereupon it isrinsed with water and dried in ambient air. It is then dipped in anaqueous solution of 3-glycidoxypropyl-trimethoxysilane of a pH of 4(concentration 1% by weight, acidification with acetic acid) and driedfor 1 minute at 160° C.

The same adhesive as in Example 17 is then deposited on the assembly ofwires treated in this manner.

The adherence test is then carried out between the assembly of wirestreated in this manner and composition 2 after simple curing for 90minutes at 140° C.

The pulling force obtained is 35 daN.

Example 20 (in accordance with the invention)

The adherence test is carried out between an assembly of bare wirestreated as in Example 19 and composition 2 after overcuring for 6 hoursat 140° C. The pulling force obtained is 35 daN, that is to say there isno decrease as compared with Example 19.

Example 21 (in accordance with the invention)

An assembly of bare wires is activated by the same phosphoric acidsolution as in Example 1, at 50° C. for 30 seconds, whereupon it isrinsed with water and dried in ambient air. It is then dipped into anaqueous solution of 3-mercaptopropyl-trimethoxysilane of a pH of 3(concentration of 1% by weight, acidification with acetic acid) anddried for 1 minute at 160° C.

The adherence test is then carried out between the assembly of wirestreated in this manner and composition 1 after simple curing for 60minutes at 150° C.

The pulling force obtained is 25 daN.

Example 22 (in accordance with the invention)

The adherence test is carried out between an assembly of bare wirestreated as in Example 21 and composition 1 after overcuring for 6 hoursat 140° C. The pulling force thus obtained is 35 daN, that is to say itis better than after simple curing (Example 21).

Example 23 (in accordance with the invention)

An assembly of bare wires is activated by the same phosphoric acidsolution as in Example 1, at 50° C. for 30 seconds, whereupon it isrinsed with water and dried in ambient air. It is then dipped into a90/10 (by volume) ethanol/water solution of3-aminopropyl-methyl-diethoxy-silane (concentration of 1% by weight) anddried for 1 minute at 160° C.

The same adhesive as in Example 17 is then deposited on the assembly ofwires treated in this manner.

The adherence test is then carried out between the assembly of wirestreated in this manner and composition 2 after simple curing for 90minutes at 140° C.

The pulling force obtained is 40 daN.

Example 24 (in accordance with the invention)

An assembly of bare wires is treated as in Example 5.

The adherence test is then carried out between the assembly treated inthis manner and composition 3, after a simple curing of 60 minutes at140° C.

The pulling force obtained is 32 daN.

Example 25 (in accordance with the invention)

The adherence test is carried out between an assembly of bare wirestreated as in Example 24 and composition 3 after overcuring for 6 hoursat 140° C.

The pulling force obtained is 30 daN, that is to say there ispractically no decrease as compared with Example 24.

Example 26 (in accordance with the invention)

An assembly 19.18 (bare wires) is treated as in Example 17, except thatthe treatment with the phosphoric acid solution is effected for 15seconds at 70° C. The adherence test is then carried out between thisassembly treated in this manner and composition 4, the formula of whichis as follows:

    ______________________________________                                               Natural rubber                                                                         100                                                                  Black N326                                                                             60                                                                   Zinc oxide                                                                             9                                                                    Antioxidant                                                                            1                                                                    Stearic acid                                                                           0.5                                                                  Sulfur   9                                                                    Sulfenamide                                                                            1                                                             ______________________________________                                    

In this formula, the definition of black, antioxidant and sulfenamideare the same as those given for formulas 1 to 3.

The adherence test is carried out after simple curing for 1 hour at 140°C. The pulling force obtained is 50 daN, that is to say it is good.

On the other hand, the assembly is treated in the manner described abovein this example, with the difference that before the silanization, afterthe treatment with the acid solution, there is also effected a treatmentof the surface with an oxygen plasma and thereupon the adherence test iscarried out with formula 4, after simple curing for 1 hour at 140° C.The pulling force obtained is 53 daN, that is to say it is slightlygreater than the preceding one, but the difference is not substantial.This shows that the treatment with the acid solution described inExample 5 permits both a good cleaning of the metal surface and a goodactivating of said surface, further activation (for instance by plasma,as described in this example) not being necessary before the silanetreatment.

Example 27 (in accordance with the invention)

An assembly 19.18 is treated in the same manner as in Example 26, withand without plasma treatment, with the difference that there is used anaqueous solution of potash and sodium carbonate (concentration in KOH: 2moles/liter; concentration in Na₂ CO₃ : 0.5 moles/liter) instead of thesolution of Example 5, and that the treatment is carried out for oneminute at about 50° C., under the joint action of ultrasonics. Thesimple curing tests carried out as in Example 26 give the followingvalues:

without plasma treatment: 38 daN;

with plasma treatment: 53 daN.

It is therefore seen that the potash solution does not permitsatisfactory activation of the surface before the silane treatment, butthat this solution permits a satisfactory cleaning of the surface sothat the plasma treatment permits a good activating of the surfacebefore the silanization and makes it possible to obtain a satisfactorypulling force.

Example 28 (not in accordance with the invention)

An assembly 19.18 is treated in the same manner as in Example 26, withand without plasma treatment, with the difference that ethanol is usedinstead of the solution of Example 5, and that the treatment is carriedout for 5 minutes at about 50° C., under the joint action ofultrasonics. The simple curing tests carried out as in Example 26 givethe following values:

without plasma treatment: 32 daN;

with plasma treatment: 32 daN.

It is therefore noted that these two values are the same, and that theyare low. The ethanol, therefore, does not make it possible to obtain anactivation of the surface before the silane treatment, nor does it makeit possible to effectively clean the surface so that the plasmaactivation treatment is ineffective.

The invention has the following advantages:

One avoids the use of organometallic compounds in the rubbercompositions, the performance of which thus remains stable; furthermore,the incorporation costs and the scarcity risks are reduced;

It is possible to use the non-oxidizable surface of the object directly,without it being necessary to effect a metal coating, for instance abrass coating;

The adherence of the stainless steel bodies, treated in accordance withthe invention, to the rubber compositions remains generally high, evenafter overcuring or after thermal aging in humid phase, while the brasscoatings, which can be used with or without cobalt compounds, frequentlyshow a large deficit after overcuring, and particularly after thermalaging in humid phase.

As shown in the examples, it is preferable to clean the metal surfacebefore effecting the activation treatment, or during said treatment,this cleaning being particularly advisable when the diameter of the wireis small, for example on the order of 0.18 mm, since the numerousdeformations, in particular the numerous wire drawings, necessary inorder to obtain this small diameter, favor the appearance of dirt on thesurface. The examples have shown the use of aqueous acid or alkalinesolutions in order to effect this cleaning, but other known methods arepossible.

The activation treatment described in the examples in accordance withthe invention employed an aqueous acid solution or a plasma, but otherknown techniques are possible.

Of course, the invention is not limited to the embodiments indicated.

We claim:
 1. A process for making a body, at least the surface of whichcomprises stainless steel, that adheres to a composition comprising atleast one rubber, said process comprising:activating the stainless steelsurface of the body, said steel containing at least 0.02% and at most0.2% carbon, at least 3% and at most 20% nickel, at least 12% and atmost 28% chromium, the sum of the nickel and chromium being at leastequal to 20% and at most equal to 35%, all of these percentages being byweight; the structure of the steel comprises at least 20% by volume ofmartensite and it is without austenite or contains less than 80% thereofby volume; treating the surface of the body with at least one startingsilane such that the surface is covered with a film constitutedexclusively, or substantially exclusively, of one or more silanescharacterized by the following formula: ##STR2## in which R representsan organic radical containing at least one function capable of reactingwith at least one element of the composition; each OR' represents agroup capable of reacting with an oxide or hydroxide of the surface ofthe stainless steel; each R" represents, independently, hydrogen, acyclic or acyclic organic radical, or a halogen; and a, which may bezero, is equal to at most 2; placing the treated surface of the body indirect contact with the composition; and curing the composition.
 2. Aprocess according to claim 1, wherein R comprises at least one functioncapable of reacting with at least one rubber of the composition, or withat least one resin contained in the composition, or with at least oneother component contained in the composition.
 3. A process according toclaim 1, wherein R is selected from the group consisting of ahydroxyalkyl, an aminoalkyl, a polyaminoalkyl, or an epoxyalkyl.
 4. Aprocess according to claim 1, wherein R is a glycidylalkyl, a haloalkyl,a mercaptoalkyl, an alkyl sulfide or an alkyl polysulfide which maycontain a silicon atom, an azidoalkyl, or a cyclic or acyclic radicalcomprising at least one double bond.
 5. A process according to claim 1,wherein each R' is, independently, hydrogen or a cyclic or acyclicorganic or organometallic radical.
 6. A process according to claim 1,characterized by the fact that when R' is an organometallic radical, itcomprises at least one silicon atom.
 7. A process according to claim 1,wherein each R' is, independently, hydrogen, an alkyl having from 1 to 6carbon atoms, and an organometallic radical comprising 1 to 6 carbonatoms and at least one silicon atom.
 8. A process according to claim 1,wherein each R" is, independently, an alkyl having from 1 to 6 carbonatoms.
 9. A process according to claim 1, wherein a is equal to zeroor
 1. 10. A process according to claim 1, wherein the silane is selectedfrom the group consisting of 3-aminopropyl-triethoxysilane,3-glycidoxypropyl-trimethoxysilane, 3-mercaptopropyltrimethoxysilane,N-beta-aminoethyl-3-aminopropyl-trimethoxysilane,3-aminopropyl-trimethoxy-silane, 3-aminoethyl-triethoxysilane, 3glycidoxyethyl-thriethoxysilane, 3-mercaptopropyl-triethoxysilane,N-beta-aminoethyl-3-aminoethyl-trimethoxysilane,3-aminobutyl-triethoxysilane, 3-aminoethyl-trimethoxy-silane,3-aminopropyl-methyl-diethoxysilane, bis-triethoxy-silylpropyltetrasulfide, bis-trimethoxy-silylpropyl tetrasulfide,p-(trimethoxysilyl)benzyl diazoacetate,4-(trimethoxysilyl)cyclohexylsulfonyl azide, and6-(trimethoxysilyl)hexylsulfonyl azide.
 11. A process according to claim10, wherein the silane is selected from the group consisting of3-aminopropyl-triethoxysilane,N-beta-aminoethyl-3-aminopropyl-trimethoxysilane,3-glycidoxypropyl-trimethoxysilane, 3-mercaptopropyl-trimethoxysilane,and 3-aminopropyl-methyl diethoxysilane.
 12. A process according toclaim 11, wherein the silane is 3-aminopropyl-triethoxysilane.
 13. Aprocess according to claim 1, wherein the activation step comprisestreating the surface with an aqueous acid solution.
 14. A processaccording to claim 1, wherein the activation step is effected at leastin part with a plasma.
 15. A process according to claim 1, wherein thesurface is cleaned before or during the activation step.
 16. A processaccording to claim 1, wherein the body of steel is a steel wire.
 17. Aprocess according to claim 1, wherein the body of steel is an assemblyof steel wires.
 18. A rubber/steel body composite comprising a rubbercomposition and a steel body, at least the surface of which comprisesstainless steel, that adheres to a composition comprising at least onerubber, said composite being obtainable by a processcomprising:activating the stainless steel surface of the body, saidsteel containing at least 0.02% and at most 0.2% carbon, at least 3% andat most 20% nickel, at least 12% and at most 28% chromium, the sum ofthe nickel and chromium being at least equal to 20% and at most equal to35%, all of these percentages being by weight; the structure of thesteel comprises at least 20% by volume of martensite and it is withoutaustenite or contains less than 80% thereof by volume; treating thesurface of the body with at least one starting silane such that thesurface is covered with a film constituted exclusively, or substantiallyexclusively, of one or more silanes characterized by the followingformula: ##STR3## in which R represents an organic radical containing atleast one function capable of reacting with at least one element of thecomposition; each OR' represents a group capable of reacting with anoxide or hydroxide of the surface of the stainless steel; each R"represents, independently, hydrogen, a cyclic or acyclic organicradical, or a halogen; and a, which may be zero, is equal to at most 2;placing the treated surface of the body in direct contact with thecomposition; and curing the composition.
 19. A composite according toclaim 18 wherein the silane is selected from the group consisting of3-aminopropyl-triethoxysilane, 3-glycidoxypropyl-trimethoxysilane,3-mercaptopropyltrimethoxysilane,N-beta-aminoethyl-3-aminopropyl-trimethoxysilane,3-aminopropyl-trimethoxy-silane, 3-aminoethyl-triethoxysilane, 3glycidoxyethyl-thriethoxysilane, 3-mercaptopropyl-triethoxysilane,N-beta-aminoethyl-3-aminoethyl-trimethoxysilane,3-aminobutyl-triethoxysilane, 3-aminoethyl-trimethoxy-silane,3-aminopropyl-methyl-diethoxysilane, bis-triethoxy-silylpropyltetrasulfide, bis-trimethoxy-silyipropyl tetrasulfide,p-(trimethoxysilyl)benzyl diazoacetate,4-(trimethoxysilyl)cyclohexylsulfonyl azide, and6-(trimethoxysilyl)hexylsulfonyl azide.
 20. A composite according toclaim 18, wherein the activation step comprises treating the surfacewith an aqueous acid solution.
 21. A composite according to claim 18,wherein the activation step is effected at least in part with a plasma.22. A composite according to claim 18, wherein the surface is cleanedbefore or during the activation step.
 23. A composite according to claim18, wherein the body of steel is a steel wire.
 24. A composite accordingto claim 18, wherein the body of steel is an assembly of steel wires.